Capacitively coupled plasma (CCP) reactors and high density plasma (HDP) reactors, such as inductively coupled plasma (ICP) reactors and electron cyclotron resonant (ECR) plasma reactors, have been widely applied in the semiconductor industry for plasma assisted material process, such as plasma enhanced chemical vapor deposition (PECVD) and plasma etch. A conventional plasma reactor, such as CCP, usually consists of two parallel plate electrodes in a chamber. The reactive nature of the discharged gas in the chamber is sustained due to the radio frequency (RF) voltage on the two electrodes. The typical pressure in the chamber ranges from 10−3–10 Torr. High voltage on the electrodes causes ion bombardment on the surface of a substrate.
HDP reactors, such as those of the ICP type, consist of two set RF coils located outside the plasma chamber. RF power is provided to the chamber by an inductive magnetic field. It is not necessary to have an electrode in the HDP reactor. In general, by applying RF bias voltage to the substrate one can independently control the ion bombardment energy in HDP.
Plasma-assisted material processes are generally carried out in a plasma chamber or reactor. To control the reaction rate across a reticle or wafer, the state of the art approach provides for the end user to adjust operational parameters. For example, the radio frequency (RF) power of the coil or neutral gas pressure may be adjusted. Additionally, the mass flow rate may be adjusted.
However, modification of the above parameters still yields a disproportionate etching or deposition rate on the surface of the substrate, i.e. sometimes significantly higher rates at the center of the substrate than at the edges. Thus, such modifications can yield, at best, only about a 2–3% uniformity across the substrate. Although this represents an improvement over processes performed without such modifications, this level of uniformity still does not meet the specifications for certain applications, such as for etching a quartz/chromium reticle.
With state of the art systems, the end user cannot do anything more to improve uniformity without sacrificing other qualities such as etch selectivity. The end user cannot make structural modifications to the reactor hardware itself, such as, adjustment of coil configuration, chamber size, and pedestal position. Such modifications could produce the desired improvements, but modifications to reactor hardware can only be made by the vendor. Thus, if heightened uniformity is to be achieved by the end-user, it should make use of conventional etching equipment.
There is thus a need for a means of attaining better plasma-enhanced material process uniformity using conventional equipment.